Continuous mass production of a fine relief pattern on a laminated transfer medium has been typically performed using techniques such as “press method” as described in PTL 1, “casting method” as described in PTL 2 and “photopolymer method” as described in PTL 3.
In manufacturing a fine relief structure by the “press method,” a resin layer on which the fine relief structure is formed is heated to a softening temperature or more, and is pressed against a relief mold (reproduction mold of the fine relief structure) to transfer the shape of the fine relief structure. In another technique, the relief mold which is heated to a softening temperature of the resin layer or more is pressed against the resin layer to transfer the shape of the fine relief structure. In either of those cases, the resin layer on which the fine relief structure is formed needs to have a processing temperature which is higher than the softening temperature. Further, the formed fine relief structure has a heat resistant temperature which is substantially the same as the minimum processing temperature.
Accordingly, in order to obtain the fine relief structure having high heat resistance, it is necessary to use a resin having a desired heat resistant temperature or more and mold the structure at a processing temperature of a desired heat resistant temperature or more. Consequently, a large amount of heat energy is required, which decreases the processing speed and the productivity.
In manufacturing of a fine relief structure by a “casting method,” a resin on which the fine relief structure is formed is heated to a melting temperature or more, and is melted and extruded onto a relief mold (reproduction mold of the fine relief structure) to transfer the shape of the fine relief structure. After the resin is cooled and has lower fluidity, it is peeled off from the relief mold.
Also in this case, the resin on which the fine relief structure is formed needs to have a processing temperature which is higher than the softening temperature. Further, the molded fine relief structure has a heat resistant temperature which is substantially the same as the minimum processing temperature.
The “photopolymer method” (2P method, photosensitive resin method) is described, for example, in PTL 3. A highly accurate fine relief pattern can be obtained by injecting a radiation curable resin into a cavity between the “relief mold” (reproduction mold of the fine relief pattern) and the “flat base” (such as plastic film), allowing it to cure by radiation, and peeling the cured film along with the base from the “relief mold”.
Optical elements obtained by this method have a relief pattern forming accuracy, heat resistance, and chemical resistance higher than those formed by “press method” or “casting method” which uses a thermoplastic resin. Further, since a radiation curable resin in a liquid form is used, a heat energy during processing is not necessary.
However, those forming methods, that is, “press method,” “casting method” and “photopolymer method” have a problem. The problem is described with reference to FIG. 7. In FIG. 7, reference number 101 denotes a laminated transfer medium. The laminated transfer medium 101 includes a carrier base 102, a bonding layer 103, a fine relief structure forming layer 104, a reflection layer 105 and an adhesive layer 106, which are stacked on the carrier base 102 in this order.
In the forming method using the laminated transfer medium 101, the fine relief structure forming layer 104 made of a resin for forming a transfer area which contains a fine relief structure on a transfer target is a continuous layer as shown in FIG. 7. Accordingly, in a transferring process of the laminated transfer medium 101 by using a hot stamp, a portion of the fine relief structure forming layer 104 to be transferred is cut off by melting so that a desired fine relief structure is transferred onto the transfer target via the adhesive layer 106. Since the breakability of the laminated transfer medium 101 which includes the fine relief structure forming layer 104 depends on a breaking strength of the resin used for the fine relief structure forming layer 104, transfer burrs or transfer defect occurs during thermal transfer, for example, at a position indicated by the dotted line in FIG. 7, leading to lowering of non-defective rate.
FIGS. 8A-8C show that transfer burrs or transfer defect occurs during transfer using the conventional laminated transfer medium 101. That is, transfer burrs or transfer defect occurs in the vicinity of an interface between a pressurized bonded area and a non-pressurized area which is indicated by A in FIGS. 8A-8C during a peeling process as indicated by A′ in FIGS. 8A-8C.